Apparatus for casting a holding block on an ophthalmic lens

ABSTRACT

The ophthalmic lens blank finished on one face is covered with a mounting member of which the wall covering the finished face of the blank is shaped to act as a bearing means for positioning the lower contour of the mould of the holding-block casting device and permitting the penetration, between said finished face of the blank and the mounting member, of the low-melting alloy cast by the holding-block casting device. After the casting operation, the mounting member remains incorporated in the block-supported blank except for a centering strip surrounding the cylindrical edge of the blank, said strip being removed by pulling a gripping member and tearing circumferentially a circular bridge portion of moderate thickness, before fitting the block-supported blank on the machine for surfacing, grinding or shaping the unfinished face of the blank.

[ 1 Feb. 111, 1975 APPARATUS FOR CASTING A HOLDING BLOCK ON AN OPHTHALMIC LENS Serge Legendre, Epinay Sur Seine, France [75] Inventor:

[73] Assignee: Essilor international (Compagnie Generale dOptique), Joinville Le Pont, France 22 Filed: May 21,1973

21 Appl. NO.Z36I,971

[30] Foreign Application Priority Data May 29, 1972 France 72.19131 {52] US. Cl 164/334, 51/216 LP, 164/112 [51] Int. Cl 322d 19/00 [58] Field of Search 425/808; 51/216 LP;

3.353.307 11/1967 Sarofeen ..5l/2l6 LP Primary ExaminerFrancis S. Husar Assistant Examiner-lohn E. Roethel {57] ABSTRACT The ophthalmic lens blank finished on one face is covered with a mounting member of which the wall covering the finished face of the blank is shaped to act as a bearing means for positioning the lower contour of the mould of the holding-block casting device and permitting the penetration, between said finished face of the blank and the mounting member, of the lowmelting alloy cast by the holding-block casting device. After the casting operation, the mounting member remains incorporated in the block-supported blank except for a centering strip surrounding the cylindrical edge of the blank, said strip being removed by pulling a gripping member and tearing circumferentially a circular bridge portion of moderate thickness, before fit- [56] References Cited ting the block-supported blank on the machine for UNITED STATES PATENTS surfacing, grinding or shaping the unfinished face of 1,952,373 3/1934 Hill 51/216 LP he blank. 2,304,984 12/1942 Wood 249/91 X 3,330,331 7/1967 Duckwall et a1 51/216 LP x 9 Chums 5 Drawing Flgul'es 13 11 21 a1 111 12 21 s T 7- l 1' 1' g 2 11 a s l r 211 l 25 PATENTEUFEBI 1 I975 SHEET 10F 2 APPARATUS FOR CASTING A HOLDING BLOCK ON AN OPHTHALMIC LENS BACKGROUND OF THE INVENTION The present invention relates to the shaping of the second face of an ophthalmic lens blank by means of a holding block cast in a suitable mould, after the shaping of the first face.

The essential object of this invention is to warrant an easy and accurate fixing, on a semi-finished blank of ophthalmic lens, notably a blank of which the finished or first face is not spherical (such as toroidal, progressive, non-toroidal, or non-spherical), a metal block for subsequently mounting or blocking this blank in a conventional surfacing machine in which the other face is eventually finished.

It is known to make such metal blocks by casting a low-melting metal into the mould of a casting device.

A very accurate positioning of the mould in relation to the reference axes of the lens blank, i.e., in relation to the first finished face must be obtained in order to ensure the necessary precision of the subsequent operations such as edge-shaping or grinding and trimming.

Moreover and preferably, it is desirable that an ordinary casting and blocking device can be utilized as such and without bringing any modification thereto, irrespective of the nature of the surface of the finished face of the lens blank.

A known proposition for solving this problem and meeting these requirements consists in providing for each type of device to be blocked a set of adaptor rings having one face shape to accommodate the finished face of the blank and the other face shaped to adapt itself to the blocking device to be used. This solution makes it necessary for the surfacing operator to have at his disposal a considerable stock of adaptor rings and obviously this stock must further be increased or replaced with another one if the operator utilizes several types of blocking devices or changes the lens model to be manufactured. Moreover, the positioning of the ring in relation to the lens blank is relatively inaccurate and may become accidentally misadjusted during the handling preceding the block casting operation.

SUMMARY OF THE INVENTION This invention relates to an improved method of blocking and casting an ophthalmic lens blank finished on one face only, which consists essentially in fixing to the blank by means of the metal fused during the casting operation a mounting member formed with bearing surfaces adapted to engage the mould clamping surfaces of the casting device.

The present invention is also concerned with the mounting member necessary for carrying out this method.

BRIEF DESCRIPTION OF THE DRAWING The features and advantages of this invention will appear more completely as the following description proceeds with reference to the accompanying drawings illustrating diagrammatically by way of example a typical mounting member made oftransparent material; in the drawings:

FIG. 1 is a perspective view showing the mounting member fitted to an ophthalmic lens blank, one portion of the mounting member being broken away to illustrate more clearly its mode of engagement of the blank;

FIG. 2 is a plan view from above of the same assemy;

FIG. 3 is a section taken along the line Ill-Ill of FIG.

FIG. 4 is a perspective view showing on a larger scale the right-hand portion of the assembly shown in FIG. 3; and

FIG. 5 is a sectional view similar to FIG. 3 showing the blank and the metal block fastened thereto by casting.

DESCRIPTION OF THE PREFERRED EMBODIMENT The mounting or reinforcing member 10 comprises at least one bearing element or portion 11 adapted to engage, or bear on, the finished face 14 of the ophthalmic lens blank 13, shaped to accommodate said face, and opposite this bearing portion 11 a part-spherical, tapered or flat seat 12 engageable by the mould of the block casting device or machine; the mounting member further comprises means for detachably assembling same to the blank 13.

These means may consist for example of a cylindrical skirt l5 bearing with a slight clamping effect, with its inner face, against the cylindrical circumferantial surface 16 of the lens blank. In this case, they act as centering means to said mounting member, and complementary means are advantageously provided for obtaining a proper angular setting, for example in the form of an inner radial projection 18 of said skirt which engages a notch or groove 19 formed to this end in the edge of the lens blank 13. Thus, "the reference axes of the blank are positioned very easily and conveniently. notably in relation to the axis of its part-spherical seat 12 or to an axis connected to the plane seat, if any.

In the selected form of embodiment illustrated by way of example the bearing elements or portions II are three in number and rigid with an annular convex portion 20 formed with a central aperture 21 permitting the access to the finished face 14'; this annular convex portion 20 is connected to the cylindrical skirt 15 by means of a continuous bridge portion 22 of moderate thickness and, therefore, adapted to be torn off very easily. These bearing faces project from the annular portion, on the face thereof which is adjacent to the inner face of the cylindrical skirt, and the opposite face of said annular portion constitutes a seat 12 which, from a part-spherical or tapered surface, centered to the axis of the aforesaid skirt, is adapted to receive the mould of the block casting machine. One of the bearing elements lla has for example a greater area than the other two llb and registers with the projection 18 carried by the skirt, these other two faces llb being disposed symmetrically in relation to the first one Ila and lying substantially on one diameter of said annular con vex portion 20.

In the vicinity of said projection 18 the skirt [5 comprises an incipient or starting of tear 24 and, adjacent the latter, a gripping lug 25.

The mounting or reinforcing member 10 is positioned on the lens blank by engaging the skirt 15 around the edge 16 of said blank, the projection 18 fitting into the notch 19 while the bearing faces Ila and llb engage the finished face 14 of blank 13. Thus, the aperture 21 gives access to the central portion of the finished face of this blank, and between the annular portion 20 and the finished face of the blank there remains an annular gap 27 interrupted only by the bearing faces 11a and 11b, and bounded on its outer periphery by the inner surface of skirt 15.

The mounting member is advantageously obtained by injecting a suitable plastic material such as polyethylene into a suitable mould (not shown). lts shape is such that after positioning this member on the blank 13 the axis of symmetry of the spherical, tapered or flat seat 12 is substantially coincident with the blank axis, notably to the axis of the face 26 to be shaped and finished.

To simplify the positioning of said mounting member 10 and avoid any risk of error likely to arise notwithstanding the presence of the reference projection or rib l8 and its matching notch 19, it is advisable to make this member 10 of transparent or translucent material nad to limit the opposite bearing elements llb by means of a pair of radial faces 28 disposed on a common diameter of this member which must be coincident with the mounting diameter of the blank. Thus, any positioning error will be noticed immediately by the operator.

On the other hand for the final shaping operation it may be necessary to take due consideration of a cylindrical and/or prismatic effect implying an angular shifting of the mounting diameter in relation to the reference diameter of the casting machine. To facilitate this operation the annular portion 20 is provided with outer peripheral radial reference marks 30 or any other similar graduations or scales which can be seen by the operator through the blank 13 to enable the operator to properly position the assembly of said blank 13 and said mounting member 10 in the casting machine. Having completed this adjustment, the operator will see that the edge 32 of mould 33 (FIG. 3) engages throughout its length the seat 12. Then, the metal of the casting block is allowed to flow into the mould to fill up all the spaces and interstices left between this mould and the blank, notably the space 27.

When the block metal has set, it is easy to separate the skirt from the remaining portions of the reinforcing or mounting member by pulling the lug 25 and tearing the starting of tear 24 and the thin bridge portion 22.

Thus, the assembly shown in FIG. 5 is obtained; this assembly comprises a block 35 adhering to the blank 13 throughout the finished face 14 thereof, except for the small marginal surface occupied by the bearing elements 11a, 11b, at least most of the annular portion remaining trapped in this block 35. This assembly is then easily mounted in a surfacing or finishing machine, exactly as in the case of a lens holding block obtained according to the conventional technique.

Advantageously, the height of the skirt 15 may be such that it projects beyond the edge of the nonfinished surface 26 of the lens blank provided with the reinforcing or mounting member 10, in order to protect this edge against shocks; on the other hand, this skirt 15 or the seat 12 may project somewhat above the finished face 14, notably in the most frequent case in which this face is convex, so as to protect this face likewise.

The mounting member 10 fitted to the blank 13 constitutes a very convenient packing element for handling or delivering this blank.

Although the above description refers essentially to a typical form of embodiment of the present invention, it will readily occur to those skilled in the art that various modifications and changes may be brought thereto without departing from the basic principle of the present invention.

What is claimed is:

1. Mounting member for use in casting a holding block on an ophthalmic lens blank finished on one face only, and adapted for fitting to the blank through centering means, means for fixing the mounting member on said blank in the angular direction, and means for engaging the finished face of said blank, said mounting member having a substantially annular configuration with an annular portion adapted to engage the finished face of the blank, said centering means comprising a cylindrical skirt forming a downward extension of said annular portion and adapted to engage with a slightly clamping force the outer cylindrical edge of the blank, and said means for fixing the blank in the proper angular direction comprising a projection carried by said skirt and engageable in a matching notch formed in the edge of said blank.

2. Mounting member according to claim 1, wherein said means for engaging the finished face of said blank comprises at least one bearing element projecting from the underside of said annular portion.

3. Mounting member according to claim 2, wherein the upper surface of said annular portion is shaped to constitute a spherical seat adapted to be engaged by a corresponding clamping surface of a block casting mold.

4. Mounting member according to claim 2, wherein the upper surface of said annular portion is shaped to constitute a tapered seat adapted to be engaged by a corresponding clamping surface of a block casting mold.

5. Mounting member according to claim 2, wherein said member is made of plastic material.

6. Mounting member according to claim 5, wherein said plastic material is a transparent plastic material.

7. Mounting member according to claim 6, wherein for positioning said member in proper angular relationship in a block casting mold it comprises a circular graduated scale visible on said annular portion through said blank.

8. Mounting member according to claim 7, wherein the skirt is connected to said annular portion through a thin bridge portion and has formed therein a transverse starting of tear having a gripping lug extension adapted, when pulled by an operator after completing the casting operation, to strip the edge of the blank.

9. Mounting member according to claim 8, wherein said member is adapted to act as a packing for protecting an ophthalmic lens blank finished on one face. 

1. Mounting member for use in casting a holding block on an ophthalmic lens blank finished on one face only, and adapted for fitting to the blank through centering means, means for fixing the mounting member on said blank in the angular direction, and means for engaging the finished face of said blank, said mounting member having a substantially annular configuration with an annular portion adapted to engage the finished face of the blank, said centering means comprising a cylindrical skirt forming a downward extension of said annular portion and adapted to engaGe with a slightly clamping force the outer cylindrical edge of the blank, and said means for fixing the blank in the proper angular direction comprising a projection carried by said skirt and engageable in a matching notch formed in the edge of said blank.
 2. Mounting member according to claim 1, wherein said means for engaging the finished face of said blank comprises at least one bearing element projecting from the underside of said annular portion.
 3. Mounting member according to claim 2, wherein the upper surface of said annular portion is shaped to constitute a spherical seat adapted to be engaged by a corresponding clamping surface of a block casting mold.
 4. Mounting member according to claim 2, wherein the upper surface of said annular portion is shaped to constitute a tapered seat adapted to be engaged by a corresponding clamping surface of a block casting mold.
 5. Mounting member according to claim 2, wherein said member is made of plastic material.
 6. Mounting member according to claim 5, wherein said plastic material is a transparent plastic material.
 7. Mounting member according to claim 6, wherein for positioning said member in proper angular relationship in a block casting mold it comprises a circular graduated scale visible on said annular portion through said blank.
 8. Mounting member according to claim 7, wherein the skirt is connected to said annular portion through a thin bridge portion and has formed therein a transverse starting of tear having a gripping lug extension adapted, when pulled by an operator after completing the casting operation, to strip the edge of the blank.
 9. Mounting member according to claim 8, wherein said member is adapted to act as a packing for protecting an ophthalmic lens blank finished on one face. 